The present invention relates to measuring devices for contactless determination of relative angular position.
A measuring device for contactless determination of relative movement between a rotor and a stator is known, in which a main gap is provided between the stator and the rotor, at least one stator air gap is provided in the stator, at least one magnetic field sensing element is provided in the at least one stator air gap and at least one ring magnet is arranged in the rotor with magnetic polarization aligned in the radial direction.
A measuring device of this type is described in French Published Patent Application FR-OS 90 15 223, in which a stator and rotor move relative to each other. A comparatively small air gap is found between the stator made from magnetically conductive material and the rotor. A first ring-shaped permanent magnet which is radially polarized is arranged in the rotor over an arc length of 180.degree.. In addition, a second ring-shaped permanent magnet polarized magnetically in the opposite sense extends similarly over a 180.degree. portion of the stator. Furthermore the stator has two stator air gaps arranged diametrically opposite to each other. A Hall sensor is arranged in at least one of these stator air gaps. The strength of the magnetic field passing through the Hall sensor changes on rotation of the rotor relative to the stator. This change of magnetic field produces a measurement signal proportional to the size of the rotational motion. The linear measurement range of this measuring device is however limited to a size of about .+-.75.degree.. Furthermore with a measurement range of about 150.degree. the rotor is arranged relative to the stator so that the null point of the induction is in the center of the angular range. Because of that, one obtains measurement signals with a minimum measurement error in the center of the measurement range and measurement signals with correspondingly larger measurement errors at the ends of the measurement range.